The invention pertains to a control system for liquid ring vacuum pumps or the like.
The suction ability of a liquid ring vacuum pump depends on the operating liquid. Where water is used as the operating liquid the suction ability of the vacuum pump can be influenced to a significant extent by adjusting the temperature of the water. In particular at high vacuum levels, the lower the temperature of the operating liquid, the better the results. Therefore cooling the circulating operating liquid is necessary. When water is used as the operating liquid, cooling is normally done by removing part of the heated liquid from the operating liquid circuit and replacing it with cool, fresh liquid from the supply line. Accordingly, the operation of a water-ring vacuum pump can consume considerable amounts of fresh water which thereby affects the operating costs.
In utilizing liquid ring vacuum pumps in a process control system it is necessary to measure certain parameters and control certain variable characteristics. In particular it is necessary to control the output variable parameters of the pumps such as capacities, pump pressures, etc. Control in the past has been accomplished by turning pumps on and off, by adjustment of throttling valves or other control devices.
Because these types of controls are usually associated with significant maintenance and energy costs, it has previously been proposed to achieve the control tasks in modern plants on centrifugal and piston pumps by utilizing stepless or continuous control of a pump's rotative speed. Energy consumption is thereby minimized.